1. Field of the Invention
The present invention is generally related to an improved marine propulsion system and, more specifically, to a marine propulsion system that utilizes a jet pump having a significantly improved flow rate which is achieved by certain advantageous configurations of its inlet and outlet structures.
2. Description of the Prior Art
Most marine propulsion systems utilize either an open propeller configuration or ajet drive configuration (i.e. a water jet). Open propellers are used with outboard, stem drive, and inboard systems. Jet drives or jet pumps, which incorporate a shrouded impeller, are typically used in jet boats, personal watercraft, and certain outboard motors that are equipped with a jet pump in place of an open propeller. Both the open propeller system and the jet pump system are well-known to those skilled in the art.
Both types of marine propulsion systems exhibit certain advantages and certain disadvantages. In a typical open propeller system, the propeller extends downward below the hull of a boat and damage can be caused if the propeller strikes a submerged object. Jet drives do not usually exhibit this disadvantage but typically are less efficient in operation and, when equipped with similarly sized engines, typically do not achieve the same maximum speed as an open propeller system.
In addition to having a lower operating efficiency and a lower maximum speed, jet drives known to those skilled in the art also exhibit certain disadvantageous spatial requirements. Most applications of jet drives require the engine to be placed in front of the pump. This utilizes valuable space in the central portion of the boat that could otherwise be used for seating or storage.
The limitation on the maximum speed for most jet drives is caused by limited water flow through the pump. As a result, to achieve a performance similar to an open propeller system, larger and more powerful engines must be used with jet drives. This, in turn, increases the cost of the propulsion system because the more expensive, higher horsepower engines are needed to achieve similar results to open propeller systems with much smaller engines.
Another difficulty that exists with most known jet drive propulsion systems is that the steering capability is severely limited under certain circumstances. Watercraft with jet drive propulsion systems can be stopped in two ways. First, the speed of the engine can be reduced by a manual throttle selection to slow the engine and allow the speed of the watercraft to decrease as a result of the friction between the hull and the surrounding water. In addition, certain jet propulsion systems are provided with a reverse gate which can be lowered behind the outlet to redirect the water and, in some cases, to create a reverse thrust to more rapidly slow the watercraft. This gate is referred to as a "bucket" or "clam shell" and is generally well-known to those skilled in the art.
When the engine of a jet propulsion system is decelerated, as during some braking maneuvers, the flow of water from the outlet is significantly reduced and, as a result, the steering capabilities of the watercraft are severely restricted. When the gate is used for braking purposes, the resulting effect on steering can be opposite to that which is normally expected. As a result, most watercraft with jet propulsion systems have little or no braking capability and, even when this capability is provided, the ability to properly steer the watercraft is severely compromised.
U.S. Pat. No. 3,982,497, which issued to Caron on Sep. 28, 1976, describes a jet-propelled powerboat. The powerboat has a tunnel drive and a propeller which is external to the boat. The boat described in this patent is fiberglass with the front rounded to prevent cracking when docking or otherwise striking an object. The cockpit is surrounded with a raised deck on all sides, including the rear, and also by rails on the inner portion of the deck sides. This patent shows in its FIGS. 3 and 5 views of the inlet opening of a jet pump which are helpful in comparison to the present invention described below.
U.S. Pat. No. 5,577,941, which issued to Chartier on Nov. 26, 1996, discloses a marine jet drive weed grate. The weed grate has a plurality of cantilever tines extending rearwardly along the water intake. They have suspended aft end tips spaced from the aft end of the water intake such that weeds and debris may slide rearwardly along and then off of the cantilever tines without clogging. The weed grate is shaped to cover the inlet opening of a jet drive propulsion system and is thus illustrative of the prior art.
A document entitled "Waterjet Propulsion Latest Developments," published by The Royal Institution of Naval Architects and presented at an International Symposium in London on Dec. 1, 1994, discusses several important factors in the development of waterjet systems. In that paper, its authors, John G. Stricker, Alan J. Becnel, and John G. Purnell, describe several water jet designs including an advanced amphibious assault vehicle (AAAV). A propulsion system demonstrator (PSD) is described and illustrated in the first figure of the paper. In that figure, a water jet is shown driven by a hydraulic motor which rotates an impeller. The outlet opening of the water jet appears to have a diameter approximately equal to the diameter of the impeller blades. Steering of a watercraft is accomplished by providing two or more water jets and using variations in the thrust of the water jets to maneuver the vehicle. In the paper no rudder or nozzle is discussed. The propulsor described in this document is intended for low speed operation with heavy loads. For example, the tested prototype described in the paper fed a diameter of 16.1 inches and a power of approximately 500 horsepower at 16 miles per hour.
Report SIT-DL-83-9-2362, dated August 1983, by the Stevens Institute of Technology for the Defense Logistics Agency of the Defense Technical Information Center of the Department of Defense is titled "Model Test of a Waterjet Propulsion System for High Speed Amphibians" by F. Thomas Korsmeyer. The report describes a water jet that was designed for evaluation in a 15 foot manned test craft. The goals of the model experiment were to determine the resistance of the test craft, to characterize the model propulsion system, and to use the characterization to reflect on the merits of the water jet design method used for the manned test craft.
Report SIT-DL-85-9-2518, published in March 1985 by the Stevens Institute of Technology for the Defense Logistics Agency of the Defense Technical Information Center of the Department of Defense is titled "Design Procedures for Low Speed Waterjets Suitable for Application in Amphibious Vehicles" and was written by John K. Roper. The paper describes a manned test craft that was constructed in order to evaluate a 14 inch diameter water jet unit at vehicle speeds up to 25 miles per hour in water. Among other things, the report concluded that a 1.0 area ratio impeller shows evidence of cavitation inception under certain circumstances, whereas two larger area impellers show no such evidence under certain condition. The inlet opening of the device was 19.5 inches and was selected to minimize the overall length of the system since trial results showed no consistent penalty associated with the shorter inlet length.
U.S. Pat. No. 5,472,359, which issued to Allbright Jr. et. al. on Dec. 5, 1995, describes an enclosed shaft system for a marine jet propulsion drive. The system provides an improved lubrication and coolant system over current designs. The preferred embodiment contemplates the utilization of an enclosed shaft system wherein the drive propeller drives a portion of the water passing through the tunnel drive through a water intake. The water is filtered and directed to a fitting where a portion of the water is directed to the engine for cooling and the remaining water is directed to the base of the shaft housing. U.S. Pat. No. 5,472,359 shows a cross-sectional area of a water jet.
U.S. Pat. No. 3,263,643, which issued to Tattersall on Aug. 2, 1966, discloses a vehicle operable over water. The invention relates to systems that operate by taking in water, energizing it, and then expelling it. It relates specifically to vehicles known as Hovercraft by those skilled in the art.
U.S. Pat. No. 33,165, which was reissued to Whitehead on Feb. 13, 1990, describes a boat hull with a flow chamber. The hull has a two-stage flow chamber. The first stage chamber starts approximately amidships as a V-shaped fairing upward at a shallow angle and flattening out approximately halfway to the stern. The second stage flow chamber starts at the end of the forward flow chamber curving upward at a greater angle than the first stage and curving downward slightly at the stern.
U.S. Pat. No. 4,088,091, which issued to Smith on May 9, 1973, discloses a fin assembly for powerboats. The fin structure is intended for mounting in an opening in the hull of a powerboat having an elongated rectangular panel connected between the base edges of a pair of elongated fins. Each fin has a base edge, a leading edge, and a trailing edge. These are joined to the elongated rectangular panel to locate the pair of fins in substantially parallel alignment in order to form a channel adapted to receive a propeller and a propeller shaft therein with the propeller in proximity of the trailing edges. The trailing edge of each fin projects from one end of the base edge beyond the outer most extremities of the propeller received in the channel. A rudder may be attached to each trailing edge of the fins and a V-drive unit may be added to reverse the longitudinal direction of the transmission power trained between the propeller shaft and the engine within the hull.
U.S. Pat. No. 3,589,325, which issued to Tattersall on Jun. 29, 1971, describes a method and apparatus for steering a marine craft. The craft is fitted with a water jet propulsion unit having a rudder disposed adjacent the outlet of the unit so as to influence the direction taken by water discharged from the outlet. The rudder, besides being pivotal about an axis passing through the plane of its surface, is also rotatable about an axis passing through the outlet of the unit. When executing a turn, the rudder is not only pivoted to execute the turn but is also rotated, in the general direction of the turn, so as to create an upward component of force on the rudder which tends to cause the craft to bank into the turn.
U.S. Pat. No. 3,598,080, which issued to Shields on Aug. 10, 1971, describes a monoshaft propeller water jet. The propulsion system of the water jet provides a semi-submerged super cavitating propeller rotating coaxially with water jet producing impellers mounted on the same shaft.
The United States patents described above are hereby explicitly incorporated by reference herein.
As described above, known pumps for jet propulsion systems exhibit significantly lower efficiencies of operation than equivalently sized open propeller systems. There are several reasons for this decreased operational capability. First, known jet pumps use outlet openings which are tapered and significantly smaller in diameter than the effective diameter of the impeller blades within the pump. This reduction in size at the outlet opening severely restricts the flow of water from the pump and increases the resistance to that flow of water. Typically, the reduced diameter of the outlet opening restricts the flow of water through the pump to a magnitude significantly less than that which the impeller could otherwise pump if the nozzle restriction did not exist. Another reason for the decreased operational efficiency of jet pumps is the restrictive configuration of the inlet opening. Simply stated, the impeller of the typical jet pump has the capability of driving a significantly higher quantity of water (i.e. mass flow) through the pump than can be efficiently drawn into and through the inlet opening toward the impeller and expelled through the outlet opening.
A third adverse effect on jet pump efficiency is the need for most known pumps to raise, or lift, water from the inlet to the location of the impeller. Energy must be expended to lift the water from the inlet opening to the height of the impeller which is typically located a significant distance from the bottom of the hull. This required work decreases the power that is available from the engine to propel the watercraft.
Another factor that reduces the fuel economy of most known jet drive propulsion systems is the fact that the engine is connected directly to the impeller and the impeller must therefore rotate continually even though the watercraft is not moving. In other words, as long as the engine is running, the impeller is rotating and attempting to force water through the pump even though that water is then merely redirected by a reversing bucket or clamshell in such a way as to prevent actual movement of the watercraft. This results in a significant waste of energy and a resulting decrease in fuel economy.
It would therefore be significantly beneficial if a marine propulsion system could be developed which utilizes a jet pump that does not exhibit the disadvantageous characteristics of lower operational efficiency, reduced maximum speed, limited acceleration capability, inconvenient spatial requirements within the watercraft, and steering difficulties during braking and reversing operations.